Recording tape cartridge

ABSTRACT

A metal plate of a recording tape cartridge is provided with a tapered portion at an outer circumference thereof. In a state in which the metal plate is attached at a fixed-side mold plate of a metal mold for molding a reel hub and a lower flange, a gap is formed between the tapered portion and the fixed-side mold plate. During molding, molding material flows into the gap. Because of this gap, an annular pawl portion is formed at the reel hub, which annular pawl portion integrally joins the metal plate with the reel hub by sandwiching the metal plate via the tapered portion.

This is a divisional of application Ser. No. 10/180,305 filed Jun. 27,2002 now U.S. Pat. No. 6,736,345; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording tape cartridge forrotatably accommodating a reel on which a recording tape is wound.

2. Description of the Related Art

In a conventionally known type of recording tape cartridge for arecording medium for use as an external storage device of a computer orthe like, a single reel, on which a recording tape such as a magnetictape is wound, is rotatably accommodated in the recording tapecartridge.

A magnetic tape is used, for example, for storing computer data. Thetape cartridge is structured so as to prevent the magnetic tape, whichmay contain important information, from jamming or the like, and frombeing unwound unintentionally when not in use, such as during storage orthe like.

The reel comprises a reel hub and upper and lower flanges, which aredisposed at both ends of the reel hub. As shown in FIG. 29, a reel hub500 and a lower flange 502 are integrally molded and, after the molding,an upper flange 504 is welded to the reel hub 500 to form a reel 506.

A magnetic tape can be wound on the reel hub 500, and width-directionalend portions of the wound-on magnetic tape are retained by the upper andlower flanges 504 and 502.

As shown in FIGS. 29 and 30, the reel hub 500 is provided with a drivengear 508, which meshes with a driving gear for transmitting drivingforce from a drive-side driving device (not shown).

At an inner side of the driven gear 508 is disposed a metal plate 510for magnetic attachment. The metal plate 510 is magnetically attractedby a magnet disposed at the drive-side driving device, thus preventingmisalignment of the axis and keeping the meshing state of the drivengear 508 and the driving gear. However, because the reel hub 500 isprovided with the driven gear 508, the metal plate 510, and the like,variations of pressure during the molding may affect the lower flange502 molded integrally with the reel hub 500, reducing flatness of thelower flange 502, and this may be a cause of surface-runout in thedrive. Further, because the flatness of the lower flange 502 is lowered,roundness of the reel hub 500 deteriorates.

The metal plate 510 is integrally molded with the reel hub 500 and thelower flange 502 inside a metal mold which molds the reel hub 500 andthe lower flange 502. Three through-holes 512 for joining the metalplate 510 to the reel hub 500 are formed at regular intervals in themetal plate 510 on a concentric circle thereof. During molding, amolding material flows into the through-holes 512 to fix the metal plate510 to the reel hub 500.

In the metal mold, a position corresponding to an inner circumferentialportion of the reel hub 500 is a gate position. When the reel hub 500and the lower flange 502 are molded, the molding material flows in aspace defined by the metal mold from the position corresponding to theinner circumferential portion of the reel hub 500 towards positionscorresponding to a distal portion of the reel hub 500, and in radialdirections towards positions corresponding to an outer circumferentialportion of the lower flange 502.

When the molding material flows into the through-holes 512 formed in themetal plate 510, air in the through-holes 512 causes friction thatresists the molding material. Therefore, comparing with a case in whichthe molding material flows around the metal plate 510, the pressure isincreased. This causes variations in the pressure in a cavity 516, anddisturbs stress balance.

Because the stress balance is disturbed when the molding material isfilled, the disturbed stress balance is manifested as residual stressafter the molding, and causes deformation of the reel hub 500 and thelower flange 502 shown in FIG. 29. Therefore, there is a risk oflowering the accuracy of the reel hub 500 and the driven gear 508, andthe flatness of the lower flange 502.

Further, as shown in FIG. 31, because within the through-hole 512 (shownby arrows) moves during hardening of the molding material, wrinkles 518are produced. Particularly, if the wrinkles 518 produce differences inthe level of the outer circumferential surface of the reel hub 500 (seeFIG. 29), a winding state of the magnetic tape on the reel may bedisturbed, and magnetic surfaces at the inner and outer circumferentialsides of the magnetic tape may be scratched by the tape's edges.

SUMMARY OF THE INVENTION

In view of the aforementioned, an object of the present invention is toprovide a recording tape cartridge comprising a highly accurate reelincluding highly flat flanges. Further, there is a demand for improvingbreaking power of the reel.

In a first aspect of the present invention, a single reel, on which arecording tape is wound, is rotatably accommodated in a recording tapecartridge. The reel includes a hollow hub on which the recording tape iswound. Annular flanges are disposed at both ends of the hub for holdingwidth-directional ends of the recording tape wound on the hub. Also, ametal plate is inserted at one end of the hub.

The hub is formed such that cross-sections taken radially from an axisthereof are the same as each other. This makes flowing states of amolding material the same for the respective cross-sectional directions.Therefore, the flowing state of the molding material does not differwith circumferential position.

In the first aspect of the present invention, an annular joining devicethat joins to an outer circumference of the metal plate may be providedat the hub. By joining the outer circumference of the metal plateinserted at the end of the hub using the annular joining device,cross-sections of the hub, taken radially from the axis thereof, can bemade the same as each other.

Further, since there is no need to provide a hole or the like in themetal plate, variations in the pressure of the molding material flowingover the metal plate are small. Therefore, residual stress can bereduced, thereby improving accuracy of the hub and flatness of theflange.

Furthermore, by joining the metal plate firmly at the outercircumference thereof, the internal dimensions of a portion for joiningthe metal plate is increased compared with the case in which the metalplate is provided with holes. This means air is easier to remove andless likely to stay. Thus, no wrinkles are created on the hub and theflange.

In the first aspect of the present invention, the joining device mayinclude a joining portion provided at the end of the hub. The joiningportion surrounds an annular joined portion extending from an entireouter circumference of the metal plate, and joins the same.

In the present invention, the joining portion may be an annular pawlportion that holds the joined portion. By provision of the pawl portion,the metal plate is prevented from coming off.

In the present invention, the joined portion may join by projectingtoward a side away from the pawl portion and meshing with the hub. Thus,the metal plate is firmly fixed to the hub.

In the present invention, an annular fitting portion can be provided ina metal mold for molding the hub, and an annular fitting portion, whichfits to the fitting portion of the mold can be formed at the metalplate. Thus, the metal plate is assuredly fixed in the metal mold.

In a second aspect of the present invention, a recording tape cartridgerotatably accommodates a reel on which a recording tape is wound, andthe reel includes a hollow hub on which the recording tape is wound.Flanges are welded at both ends of the hub, and the flanges retain thewidth-directional ends of the recording tape that is wound on the hub.

Specifically, the hub and the flanges are separately molded, and theflanges are then welded at the both ends of the hub to form the reel.Separately molding the hub and the flanges allows selection of asuitable gating system, for example disc gates, and setting of optimalmolding conditions for each shape.

Therefore, compared with the case in which the hub and the flange areintegrally molded, variations in pressure of the hub can be reduced andflatness of the flanges can be improved. Further, roundness of the hubcan be improved by the improvement in the flatness of the flange.

Moreover, by welding the hub and the flange, they can be united withgreater certainty and less backlash compared with the case in which aflange and hub are provided with pawl portions for fitting to eachother, and can be united more simply compared with the case in which aflange and hub are threaded and screwed together.

In the second aspect of the present invention, a first weld boss may beprovided projecting from a welding surface, for welding to the flange,along a circumferential direction of a collar provided at an outercircumferential surface of the hub. A second weld boss may be providedprojecting from another welding surface, for welding to the otherflange, along a circumferential direction of a stepped portion providedat an inner circumferential surface of the hub.

By providing the first weld boss and the second weld boss projectingfrom the welding surfaces, the weld bosses can be fused to weld theflanges to the hub when frictional heat is generated between the flangesand the hub by vibrational energy from an ultrasonic welder. Therefore,compared with the case in which no weld boss is provided, the flangesand hub can be welded together more firmly.

In the second aspect of the present invention, a gap may be formedbetween the outer circumferential surface of the collar and the hub andan inner circumferential surface of the flange, so that residue of thefirst weld boss can run into the gap. According to the second aspect ofthe present invention, when two members are to be welded, one of thewelding surfaces is provided with a projecting weld boss, and the weldboss is fused for welding. By forming the gap between the innercircumferential surface of the flange and the outer circumferentialsurface of the collar of the hub, and allowing the residue from thewelding surface to run into the gap, the residue of the welding can beprevented from running over onto the surface of the flange.

In the second aspect of the present invention, a gap may be formedbetween a wall surface of the stepped portion and an outercircumferential surface of a boss provided at an inner circumferentialportion of the flange, so that residue of the second weld boss can runinto this gap.

In the second aspect of the present invention, instead of the first weldboss, a third weld boss may be provided at a stepped portion cut intothe outer circumferential surface of the hub, and an upper surface ofthe flange may make surface contact with a ceiling portion of thisstepped portion. In this structure, a gap is formed between a wallsurface of the stepped portion and an inner circumferential surface ofthe flange, so that residue of the third weld boss can run into thisgap. Thus, edges of the recording tape can be prevented from coming intothe gap.

In a third aspect of the present invention, a recording tape cartridgerotatably accommodates a reel on which a recording tape is wound. Thereel includes a core. An annular lower flange is integrally molded withthe core and positioned at one end side of the core.

Outside the core, a cylindrical hub, on which the recording tape iswound, is disposed and fixed at the lower annular flange (also referredto herein as “lower flange”). Further, an upper annular flange (alsoreferred to herein as “upper flange”) is fixed at the other end side ofthe core, and the upper flange and lower flange held width-directionalends of the recording tape wound on the hub.

By disposing the hub outside the core and winding the recording tape onthe hub, even if the core becomes inclined due to thermal contractionafter the molding of the core and the lower flange, the inclination ofthe core does not affect winding of the recording tape, and a highlyaccurate hub can be obtained.

In the third aspect of the present invention, the hub may include asleeve attached at an annular depression formed in the lower flange on aconcentric circle thereof. During thermal contraction after molding, thethermal contraction is effected along radial directions of the core andthe lower flange. Therefore, the annular depression follows the thermalcontraction of the core and the lower flange. By providing the annulardepression on a concentric circle of the lower flange, and fitting thesleeve in the annular depression, the axis of the sleeve is aligned withaxes of the core and the lower flange. Therefore, the axis of the sleevedoes not deviate with respect to the lower flange.

In the third aspect of the present invention, a small diameter portionmay be provided at one end side of the sleeve, and the small diameterportion may be attached to the annular depression. In this structure, ashoulder portion between the small diameter portion and a large diameterportion abuts on the lower flange. Therefore, even if there is a gapformed between the small diameter portion and the annular depression,the recording tape will not come into the gap.

In the third aspect of the present invention, the sleeve of the hub isinserted in a metal mold for molding the core and the lower flange.Thus, labor for attaching the sleeve after the molding of the core andthe lower flange can be saved. Therefore, production steps can bereduced, thereby reducing production costs.

In the third aspect of the present invention, a metal sleeve may beused. Since metals have a lower coefficient of linear expansion thansynthetic resins, use of the metal sleeve provides a highly accuratehub.

In the third aspect of the present invention, engaging portions forengaging with the upper flange and the lower flange may be provided atthe sleeve at an inner circumferential surface side thereof. In thisstructure, the recording tape is wound only on the sleeve. Therefore,even if size is irregular at engaged portions of the upper flange andthe lower flange which engage with the sleeve, this irregularity doesnot affect the winding of the recording tape.

In a fourth aspect of the present invention, the reel includes a hollowhub on which recording tape is wound, and annular flanges are disposedat both ends of the hub for holding the width-directional ends of therecording tape wound on the hub. A reel rotation gear is disposed at oneend of the hub, and a plate is disposed inside the reel rotation gear,which plate can be attracted by a magnet disposed at a drive forwriting/reading information on/from the recording tape.

A braking gear is provided at an outer circumference of one flange, andthe braking gear can engage with a braking member disposed in a casethat accommodates the reel. By providing the braking gear at the outercircumference of the flange to effect braking, unintended rotation ofthe reel when the recording tape cartridge is not in use can naturallybe prevented with certainty. Further, compared with a case in which thebraking gear is provided at a core side of the flange, required brakingforce is smaller and pitch of the braking gear can be increased.Therefore, failures such as breakage of the braking gear will not becaused. Moreover, since the braking gear is not provided at the coreside of the flange, molding accuracy of the reel can be improved.

In the fourth aspect of the present invention, the braking member isurged by an urging device in a direction in which it engages with thebraking gear. At a time when a driving gear, which is disposed at thedrive and can mesh with the reel rotation gear, meshes with the reelrotation gear, the braking member is pushed in a direction against theurging device to release engagement between the braking member and thebraking gear.

In other words, when the driving gear is not meshed with the reelrotation gear, the braking member urged by the urging device engageswith the braking gear to block rotation of the reel. On the other hand,at the same time as the driving gear meshes with the reel rotation gear,the braking member is pushed in the direction against the urging deviceto release engagement between the braking member and the braking gear.Therefore, driving force from the driving gear can be transmitted to thereel rotation gear to rotate the reel.

In the fourth aspect of the present invention, the pitch of the brakinggear may be in a range from 1 mm to 3.5 mm. As a result, the brakinggear is not easily broken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a recording tape cartridgeaccording to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of the recording tape cartridgeaccording to the first embodiment of the present invention viewed frombelow.

FIG. 3 is a sectional view of the recording tape cartridge according tothe first embodiment of the present invention and a drive-side drivingdevice.

FIG. 4 is an exploded sectional view of a reel included in the recordingtape cartridge according to the first embodiment of the presentinvention.

FIG. 5 is a perspective sectional view of a reel hub and a lower flangeof the reel included in the recording tape cartridge according to thefirst embodiment of the present invention, showing a tapered portion ofa metal plate and a pawl portion of the lower flange.

FIG. 6 is a sectional view schematically showing a metal mold formolding the reel hub and the lower flange of the reel included in therecording tape cartridge according to the first embodiment of thepresent invention.

FIG. 7 is a perspective sectional view of the reel hub and the lowerflange of the reel included in the recording tape cartridge according tothe first embodiment of the present invention, showing a stepped portionand an annular rib of the metal plate and the lower flange.

FIG. 8 is a perspective sectional view of the reel hub and the lowerflange of the reel included in the recording tape cartridge according tothe first embodiment of the present invention, showing the annular ribof the metal plate and the lower flange.

FIG. 9 is a sectional view of a recording tape cartridge according to asecond embodiment of the present invention and the drive-side drivingdevice.

FIG. 10 is an exploded sectional view of a reel included in therecording tape cartridge according to the second embodiment of thepresent invention.

FIG. 11 is an enlarged view of an annular flange provided at a hub and alarge diameter portion provided at a lower flange included in the reelincluded in the recording tape cartridge according to the secondembodiment of the present invention.

FIG. 12A is an enlarged view of the annular flange provided at the huband the large diameter portion provided at the lower flange included inthe reel included in the recording tape cartridge according to thesecond embodiment of the present invention, before the lower flange iswelded to the hub.

FIG. 12B is an enlarged view of the annular flange provided at the huband the large diameter portion provided at the lower flange included inthe reel included in the recording tape cartridge according to thesecond embodiment of the present invention, when the lower flange iswelded to the hub.

FIG. 13A is an enlarged view of a small diameter portion provided at thehub and a boss provided at an upper flange included in the reel includedin the recording tape cartridge according to the second embodiment ofthe present invention, before the upper flange is welded to the hub.

FIG. 13B is an enlarged view of the small diameter portion provided atthe hub and the boss provided at the upper flange included in the reelincluded in the recording tape cartridge according to the secondembodiment of the present invention, when the upper flange is welded tothe hub.

FIG. 14 is a schematic perspective view of a jig and a horn used forwelding the upper flange and the hub, and the lower flange and the hubforming the reel included in the recording tape cartridge according tothe second embodiment of the present invention.

FIG. 15 is an exploded sectional view of a modification of the reelincluded in the recording tape cartridge according to the secondembodiment of the present invention.

FIG. 16 is an enlarged view of a hub and a lower flange of themodification of the reel included in the recording tape cartridgeaccording to the second embodiment of the present invention.

FIG. 17A is an enlarged view of the modification of the reel included inthe recording tape cartridge according to the second embodiment of thepresent invention, before the hub is welded to the lower flange.

FIG. 17B is an enlarged view of the modification of the reel included inthe recording tape cartridge according to the second embodiment of thepresent invention, when the hub is welded to the lower flange.

FIG. 18A is an enlarged view of another modification of the reelincluded in the recording tape cartridge according to the secondembodiment of the present invention, before an upper flange and a lowerflange are welded to a hub.

FIG. 18B is an enlarged view of the modification of the reel included inthe recording tape cartridge according to the second embodiment of thepresent invention, when the upper flange and the lower flange are weldedto the hub.

FIG. 19A is an enlarged view of yet another modification of the reelincluded in the recording tape cartridge according to the secondembodiment of the present invention, before an upper flange and a lowerflange are welded to a hub.

FIG. 19B is an enlarged view of the modification of the reel included inthe recording tape cartridge according to the second embodiment of thepresent invention, when the upper flange and the lower flange are weldedto the hub.

FIG. 20 is an exploded perspective view of a reel included in arecording tape cartridge according to a third embodiment of the presentinvention.

FIG. 21 is an exploded sectional view of the reel included in therecording tape cartridge according to the third embodiment of thepresent invention.

FIG. 22 is a sectional view of the reel included in the recording tapecartridge according to the third embodiment of the present invention.

FIG. 23 is a sectional view of the recording tape cartridge according tothe third embodiment of the present invention.

FIG. 24 is an exploded sectional view of a modification of the reelincluded in the recording tape cartridge according to the thirdembodiment of the present invention.

FIG. 25 is a sectional view of the modification of the reel included inthe recording tape cartridge according to the third embodiment of thepresent invention.

FIG. 26 is a sectional view showing a state in which a reel hub isinclined.

FIG. 27 is an exploded perspective view of a recording tape cartridgeaccording to a fourth embodiment of the present invention.

FIG. 28 is a sectional view of the recording tape cartridge according tothe fourth embodiment of the present invention and the drive-sidedriving device.

FIG. 29 is an exploded sectional view of a conventional reel.

FIG. 30 is a bottom view of a metal plate inserted in a metal mold formolding a reel hub and a lower flange of the conventional reel.

FIG. 31 is a sectional view showing a state of a molding materialflowing in the metal mold for molding the reel hub and lower flange ofthe conventional reel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A recording tape cartridge according to a first embodiment of thepresent invention will now be described. It should be noted that, forconvenience of explanation, a direction in which the recording tapecartridge is mounted into a drive is referred to as a forward direction,and expressions such as front, back, right, left, upper and lower arebased on this direction. Further, the recording tape used is a magnetictape, and the following description is made with respect to a magnetictape cartridge.

First, an outline of the magnetic tape cartridge according to the firstembodiment of the present invention is described.

As shown in FIGS. 1-3, a magnetic tape cartridge 10 comprises an uppercase 20 and a lower case 30, which are made of synthetic resin andformed in a substantially rectangular box shape. A peripheral wall 22 ofthe upper case 20 and a peripheral wall 32 of the lower case 30 arewelded together by ultrasonic welding or the like.

Substantially cylindrical walls 24 and 34 are formed standingrespectively from inner surfaces of the upper case 20 and the lower case30. Internal diameters of the cylindrical walls 24 and 34 are slightlylarger than external diameters of an upper flange 52 and a lower flange54 of a reel 50, and the reel 50 is rotatably accommodated in thecylindrical walls 24 and 34.

Ribs 23 are provided between the cylindrical wall 24 and the peripheralwall 22 of the upper case 20, and ribs 33 are provided between thecylindrical wall 34 and the peripheral wall 32 of the lower case 30. Theribs 23 and 33 respectively connect the cylindrical wall 24 to theperipheral wall 22, and the cylindrical wall 34 to the peripheral wall32, thereby reinforcing the cylindrical walls 24 and 34.

The reel 50 comprises a cylindrical reel hub 56, and the upper flange 52and lower flange 54 disposed at both ends of the reel hub 56. The upperflange 52 and the lower flange 54 retain width-directional edges of amagnetic tape 12, which is a medium for writing and reading information,wound around the reel hub 56.

A bottom wall 58 including a hole 58A formed in the center thereof isprovided at the lower flange 54 side of the reel hub 56. An annular reelgear 60 (driven gear) is formed at a lower surface side of the bottomwall 58 projecting from the bottom wall 58.

The reel gear 60 can be exposed through a circular opening 38 providedin the center of the lower case 30 so as to mesh with a driving gear 63provided at a drive 65 and transmit rotational force to the reel 50.

An annular metal plate 62 is integrally molded at an inner side of thereel gear 60. The metal plate 60 is attracted by a magnet (not shown)disposed at the drive 65 in order to prevent axial misalignment, andthus maintain the meshing state of the reel gear 60 with the drivinggear 63.

An annular groove 64 is provided outside the reel gear 60. A rib 36,which is provided standing from a peripheral portion of the opening 38provided in the lower case 30, is inserted in the annular groove 64 sothat the reel 50 is positioned with respect to the lower case 30.

Further, an annular reel gear 70 is formed at an upper surface side ofthe bottom wall 58 of the reel hub 56. The reel gear 70 can mesh with abraking gear 82 provided at a lower surface outer circumferentialportion of a substantially disk-shaped braking member 80, which can beaccommodated in the reel hub 56.

Substantially U shaped (when viewed from above) ribs 84 (hereinafterreferred to as “U-rib”) are provided standing up from the braking member80. Also, a pair of locking pins 66, which can engage with the U-rib 84,is suspended from the center of the inner surface of the upper case 20.

Thus, the braking member 80 can move within the reel hub 56 and theU-rib 84 of the braking member 80 can move along the locking pins 66,and rotation of the braking member 80 is blocked. Therefore, when themagnetic tape cartridge 10 is not in use, the braking gear 82 of thebraking member 80 is meshed with the reel gear 70 to prevent rotation ofthe reel 50.

Further, an annular groove 86 is provided at the braking member 80outside the U-rib 84. Also, an annular projection 68 is provided at theupper case 20 outside the locking pins 66. The annular projection 68 andthe annular groove 86 hold a spring 16, which is mounted between thebraking member 80 and the upper case 20.

Thus, the braking member 80 is urged toward the reel gear 70 so that thebraking gear 82 firmly meshes with the reel gear 70, thereby assuredlypreventing unintended rotation of the reel 50.

A substantially cylindrical projection 88, which can be inserted into ahole 58A, is provided at the center of a lower surface of the brakingmember 80. Before the reel gear 60 meshes with the driving gear 63 totransmit rotational force to the reel 50, a mesh-release pin 69, whichis provided at a tip of a rotating shaft 67 of the drive 65, abuts theprojection 88 to push up the braking member 80 in a direction againsturging force of the spring 16, thereby releasing meshing between thebraking gear 82 and the reel gear 60. Thus, rotation of the reel 50 ispermitted.

As shown in FIG. 1, openings 18 and 19 are formed respectively atfront-left corners of the peripheral wall 22 of the upper case 20 andthat of the peripheral wall 32 of the lower case 30. The openings 18 and19 are provided such that the magnetic tape 12 wound around the reel 50can be drawn out.

A leader block 40 is attached at an end of the magnetic tape 12. Apulling pin (not shown) provided at the drive engages with a recess 42formed in the leader block 40, and the magnetic tape 12 is wound by awinding reel provided at the drive. At this time, the reel 50 and thewinding reel are driven to rotate synchronously, and data is written orread while the magnetic tape 12 is sequentially wound onto the windingreel.

On the other hand, when the magnetic tape cartridge 10 is not in use,the leader block 40 is locked at peripheral edges of the openings 18 and19, and the openings 18 and 19 are closed by the leader block 40.

Next, the reel of the magnetic tape cartridge 10 according to the firstembodiment of the present invention is described. It should be notedthat explanations of parts that overlap the above description areomitted.

As shown in FIGS. 4 and 5, the reel hub 56 and the lower flange 54,which form the reel 50, are integrally molded. A weld boss 72 forultrasonic welding, which has a substantially triangular cross section,is provided projecting from an end surface of the reel hub 56.

After the reel hub 56 and the lower flange 54 have been molded, theupper flange 52 is placed on top of the weld boss 72, and the weld boss72 is fused by ultrasonic waves to weld the upper flange 52 to the endsurface of the reel hub 56, thereby forming the reel 50.

The reel hub 56 and the upper flange 52 are formed using moldingmaterials which are mutually compatible. Therefore, the reel hub 56 andthe upper flange 52 can be welded together using ultrasonic waves.Examples of types of the molding materials include combinations ofresins such as PMMA and ABS, AS and ABS, and combinations ofpolycarbonates.

An inner circumferential surface of the reel hub 56 is provided with asmall diameter portion 74 at a position a step lower than the endsurface of the reel hub 56. Also, a boss 52A is formed at the upperflange 52. When the upper flange 52 is placed on top of the weld boss72, the boss 52A engages with the inner circumferential surface of thereel hub 56.

Further, when the upper flange 52 is welded to the end surface of thereel hub 56 by the ultrasonic welding, the end surface of the boss 52Aabuts on the end surface of the small diameter portion 74, therebylimiting movement of the upper flange 52 (see FIG. 3).

Thickness of the reel hub 56 is partially increased by the provision ofthe small diameter portion 74 at the inner circumferential surface ofthe reel hub 56. However, the annular groove 64 provided in the bottomwall 58 of the reel hub 56 is utilized to reduce the thickness, thethickness of the reel hub 56 is made as even as possible, and thussinking of the outer circumferential surface of the reel hub 56 can beprevented.

The metal plate 62 is disposed inside the reel gear 60. The metal plate62 is integrally molded by being inserted into a metal mold 81 formolding the reel hub 56 and the lower flange 54, shown in FIG. 6.

The metal mold 81 includes a fixed-side mold plate 83 and a movable-sidemold plate 85. The molding material is filled into a cavity 87 definedby the fixed-side mold plate 83 and the movable-side mold plate 85 in astate in which the metal plate 62 is fixed to the fixed-side mold plate83 and the metal mold 81 is clamped.

An annular depression 78 is provided at one side of the metal plate 62.When the metal plate 62 is attached at the fixed-side mold plate 83, anannular protrusion 77 formed at the fixed-side mold plate 83 fits in theannular depression 78, to position and fix the metal plate 62 to thefixed-side mold plate 83.

Further, an annular tapered portion 90 is provided, as a joinableportion, at a peripheral portion of the one end side of the metal plate62. When the metal plate 62 is attached to the fixed-side mold plate 83,a gap is formed between the tapered portion 90 of the metal plate 62 andthe fixed-side mold plate 83. At the time of molding, the moldingmaterial flows into this gap.

With this gap, as shown in FIGS. 4 and 5, an annular pawl portion 92,which serves as a joining portion joined to the outer circumference ofthe metal plate 62, is formed at the reel hub 56. In this manner, by thepawl portion 92 joining to the tapered portion 90 of the metal plate 62,the metal plate 62 is united with the reel hub 56.

Moreover, by providing the annular tapered portion 90 at the peripheralportion of the one end side of the metal plate 62 and joining thetapered portion 90 by the annular pawl portion 92, all cross-sectionalforms of the reel hub 56 taken radially from the axis of the reel hub 56can be made the same as each other. Therefore, flowing states of themolding material do not differ between circumferential directionpositions.

In addition, since there is no need to provide the through-holes 512 inthe metal plate 510 (see FIG. 29) as in the conventional technique,variations in the pressure of the molding material flowing over themetal plate 62 are small. Therefore, the residual stress can be reduced,improving accuracy of the reel hub 56 and the reel gear 60. Further,flatness of the lower flange 54 can be improved.

Further, by providing the annular pawl portion 92 for joining the outercircumference of the metal plate 62, internal dimensions of the portionfor joining the metal plate 62 are larger than in the case of providingthe through-holes 512 in the metal plate 510 (FIG. 31), and air iseasier to remove and less likely to be trapped. Thus, no wrinkles arecaused on the reel hub 56 and the lower flange 54.

It should be noted that the tapered portion 90 is provided at the metalplate 62 to improve joint condition between the metal plate 62 and thelower flange 54 for integration thereof. However, this is not intendedto limit the present invention, what is required is simply that themetal plate 62 is united with the lower flange 54 by insert molding.

For example, as shown in FIG. 7, an annular stepped portion 94A, whichserves as a joining portion, may be provided at an outer circumferentialsurface of a metal plate 94 so as to intrude into a reel hub 93. Anannular rib 94B may be provided standing from an outer circumferentialsurface of the metal plate 94 toward a movable-side mold plate of ametal mold (upward in FIG. 7), and the stepped portion 94A and the rib94B may be joined by an annular pawl portion 95.

Thus, the molding material is poured into a stepped portion defined bythe stepped portion 94A and the rib 94B, and joint condition around therib 94B is improved by increasing contact area with the lower flange 54,thus uniting the metal plate 94 with the lower flange 54.

Further, as shown in FIG. 8, simply by providing an annular rib 96A (ajoining portion) standing from an outer circumferential surface of ametal plate 96 toward a movable-side mold plate of a metal mold (upwardin FIG. 8) to join with the bottom wall 58 (joining portion) of thelower flange 54, the metal plate 96 can be joined with the lower flange54.

Furthermore, although a so-called single reel type, wherein one reel isaccommodated in the magnetic tape cartridge, is described here, this isnot intended to limit the present invention. A two-reel type, whereintwo reels are accommodated in the magnetic tape cartridge, is alsoapplicable.

Next, a reel of a magnetic tape cartridge according to a secondembodiment of the present invention is described. It should be notedthat details of the magnetic tape cartridge according to the presentembodiment are substantially the same as those of the magnetic tapecartridge according to the first embodiment, and therefore explanationthereof is omitted.

As shown in FIGS. 9 and 10, a reel hub 202, an upper flange 204 and alower flange 206 forming a reel 200 are separately molded Additionally,the upper flange 204 and the lower flange 206 may be molded as a set.After the reel hub 202, the upper flange 204 and the lower flange 206have been molded, the reel hub 202 and the upper flange 204, and thereel hub 202 and the lower flange 206 are welded by ultrasonic weldingto form the reel 200.

As shown in FIGS. 11 and 12A, a collar 208 extends from a lower edge ofan outer circumference of the reel hub 202. On an upper surface of thecollar 208, a so-called weld boss 210, which is fused by ultrasonicwaves for welding to the lower flange 206, is provided so as to projecttherefrom. A sectional form of the weld boss 210 is substantially atriangle, so it can be fused easily.

An internal diameter D₁ of the lower flange 206 is slightly larger thanan external diameter D₂ of the reel hub 202, so that a gap h is formedbetween an outer circumferential surface of the reel hub 202 and aninner circumferential surface of the lower flange 206 when the lowerflange 206 is fitted on the reel hub 202.

Further, the lower flange 206 is provided with a large diameter portion212. An internal diameter of the large diameter portion 212 is slightlylarger than an external diameter of the collar 208, so that a gap t isformed between the collar 208 and the large diameter portion 212 whenthe lower flange 206 is fitted on the reel hub 202.

Because the gaps h and t are formed between the reel hub 202 and thelower flange 206, residue of the fused weld boss 210, which is producedwhen the reel hub 202 and the lower flange 206 are welded, runs into thegaps h and t.

Thus, as shown in FIG. 12B, the residue of the welding material does notoverflow onto the surfaces of the reel hub 202 and the lower flange 206.Further, the welding can be effected not only in an axial direction ofthe reel hub 202, but also in a circumferential direction thereof,thereby providing a good welding stability.

Also, as shown in FIG. 13A, an inner circumferential surface of the reelhub 202 is provided with a small diameter portion 214 (stepped portion)at a position a step lower than the end surface of the reel hub 202. Aweld boss 216 is provided projecting from a top surface of the smalldiameter portion 214.

A boss 204A is formed at the upper flange 204. An external diameter ofthe boss 204A is slightly smaller than an internal diameter of the reelhub 202, so that a gap s is formed between an inner circumferentialsurface of the reel hub 202 and an outer circumferential surface of theboss 204A.

Thus, when the reel hub 202 and the upper flange 204 are welded, asshown in FIG. 13B, residue of the fused weld boss 216 runs into the gaps (see FIG. 13A). Therefore, the residue of the welding material doesnot run over onto the surface of the reel hub 202. Further, by makingthe residue of the welding material run into the gap s formed betweenthe inner circumferential surface of the reel hub 202 and the outercircumferential surface of the boss 204A, welding can be effected notonly in the axial direction of the reel hub 202, but also in thecircumferential direction thereof, thereby providing a good weldingstability.

It should be noted that, although the residue of the fused weld boss 216slightly overflows onto inner circumferential surfaces of the boss 204Aand small diameter portion 214, this does not affect flatness of theupper flange 204 and roundness of the reel hub 202, and therefore is nota problem.

Next, a method for welding the upper flange 204, the lower flange 206and the reel hub 202 is described.

First, for performing ultrasonic welding, a jig for fixing the reel hub202 and the like, which are placed on a stage of an ultrasonic welder(not shown), and a ‘horn’ for transmitting vibrational energy generatedby the ultrasonic welder to the upper flange 204 and the reel hub 202,and to the lower flange 206 and the reel hub 202 are necessary.

As shown in FIG. 14, the jig 218 includes a hollow-cylindricaldepression 222 whose internal diameter is substantially the same asexternal diameters of the upper flange 204 and the lower flange 206 (seeFIG. 14). A cylindrical shaft 220, whose external diameter issubstantially the same as the internal diameter of the hole 58A formedin the bottom wall 58 of the reel hub 202, is provided at the center ofthe annular depression 222.

When the upper flange 204 and the lower flange 206 are fitted in theannular depression 222 and the reel hub 202 is fitted on the shaft 220,the upper flange 204, the lower flange 206 and the reel hub 202 arecoaxially aligned.

A lower flange horn 224 is substantially cylindrical, and has a sizesuch that it can fit around the outer circumference surface of the reelhub 202 and face the collar 208. An upper flange horn 226 (see FIG. 13B)is also substantially cylindrical, and has an external diametersubstantially the same as the external diameter of the reel hub 202 andan internal diameter substantially the same as the internal diameter ofthe small diameter portion 214 of the reel hub 202.

When welding the upper flange 204 to the reel hub 202, a load applied bythe upper flange horn 226 is received by the reel hub 202, and thereforeno excessive load is applied to the upper flange 204.

In this structure, the reel hub 202 is fitted on the shaft 220 of thejig 218, the lower flange 206 is fitted in the annular depression 222and as shown in FIG. 12A, a ceiling portion 212A formed by the largediameter portion 212 of the lower flange 206 is abutted against the topof the weld boss 210 formed at the collar 208 of the reel hub 202.

In this state, the reel hub 202 and the lower flange 206 are coaxiallypositioned. Therefore, the axes of the lower flange 206 and the reel hub202 are kept aligned in spite of the presence of the gaps h and t formedbetween the outer circumferential surfaces of the reel hub 202 and theinner circumferential surfaces of the lower flange 206.

Next, as shown in FIG. 12B, the lower flange horn 224 of the ultrasonicwelder is abutted on the lower flange 206, and the vibrational energygenerated by the ultrasonic welder is transmitted to the lower flange206 via the lower flange horn 224. Thus, frictional heat is generatedbetween the lower flange 206 and the reel hub 202, and the weld boss 210(see FIG. 12A) is fused to weld the lower flange 206 to the reel hub202.

Next, the upper flange 204 is welded to the reel hub 202 (see FIG. 14).The upper flange 204 is fitted in the annular depression 222 of the jig218 shown in FIG. 14 and as shown in FIG. 13A, the end surface of theboss 204A of the upper flange 204 is abutted against the top of the weldboss 216 formed at the small diameter portion 214 of the reel hub 202,to which the lower flange 206 has already been welded.

In this state, the upper flange 204 and the reel hub 202 are coaxiallypositioned. Therefore, the axes of the upper flange 204, the reel hub202 and the lower flange 206 are kept aligned in spite of the presenceof the gap s formed between the inner circumferential surface of thereel hub 202 and the outer circumferential surface of the boss 204A.

Next, as shown in FIG. 13B, the upper flange horn 226 is abutted on theupper flange 204. Thus, the weld boss 216 (see FIG. 13A) is fused toweld the upper flange 204 to the reel hub 202, thereby forming the reel200.

As described above, by welding the upper flange 204, the lower flange206 and the reel hub 202, which are separately molded, the highlyaccurate reel 200 can be easily formed.

In other words, the upper flange 204, the lower flange 206 and the reelhub 202 can be separately molded. This allows selection of a suitablegating system (such as disc gates) and setting of optimal moldingconditions for each of the upper flange 204, the lower flange 206 andthe reel hub 202 depending on the shapes thereof. Thus, flatness of thelower flange 206 can be improved, and at the same time roundness of thereel hub 202 can also be improved.

By welding, the reel hub 202 and the lower flange 206 can be united withcertainty and without backlash, as compared with the case in which thelower flange and the hub are provided with pawl portions to be fittedwith each other, and can be united more simply as compared with the casein which the flange and the hub are threaded and screwed together.

It should be noted that although the upper flange 204 and the lowerflange 206 are separately welded to the reel hub 202 in this embodiment,welding between the upper flange 204 and the reel hub 202, and betweenthe reel hub 202 and the lower flange 206 may be performedsimultaneously by fitting the reel hub 202, the lower flange 206 and theupper flange 204 in the annular depression 222 in this order and thenabutting the upper flange horn 226 on the upper flange 204. However, inthis case, slight modifications are required to a generated frequencysetting of the ultrasonic welder, to the shape of the horn, and thelike.

Further, although the collar 208 is extended from the outercircumferential surface of the reel hub 202 for welding to the lowerflange 206 in this embodiment, the shape is not limited to the shape inthis embodiment; all that is required is that the lower flange 206 canbe welded to the reel hub 202 neatly.

For example, as shown in FIGS. 15 and 16, a small diameter portion 236is provided at an outer circumferential lower edge of a hub 228, a smalldiameter flange 232 is provided at a lower flange 230 extending from aninner circumferential surface thereof, and a weld boss 234 is providedprojecting from the small diameter flange 232.

Further, an internal diameter D₁ of the lower flange 230 is slightlylarger than an external diameter D₂ of the hub 228. When the hub 228 isfitted in the lower flange 230, a gap h₁ is formed between the outercircumferential surface of the hub 228 and the inner circumferentialsurface of the lower flange 230, as shown in FIG. 17. Also an internaldiameter of the small diameter flange 232 of the lower flange 230 isslightly larger than an external diameter of the small diameter portion236 of the hub 228, and when the hub 228 is fitted in the lower flange230, a gap t₁ is formed between the small diameter portion 236 of thehub 228 and the small diameter flange 232 of the lower flange 230. Thus,when the hub 228 and the lower flange 230 are welded together, residueof the fused weld boss 234 (see FIG. 17A) runs into the gaps h₁ and t₁,as shown in FIG. 17B.

Further, as shown in FIGS. 18A and 18B, by providing a small diameterportion 242 (stepped portion) at an outer circumferential lower edge ofa hub 240, providing a weld boss 246 projecting from a ceiling surface244 formed by a small diameter portion 242, and welding a top surface248A of a lower flange 248 thereto, so that there is no gap formed in anarea of an outer circumferential surface of the hub 240, where magnetictape will be wound, a risk of edges of the magnetic tape coming intosuch a gap can be eliminated.

In this structure, a gap t₂ is formed between the small diameter portion242 of the hub 240 and an inner circumferential surface of the lowerflange 248, so that residue of the fused weld boss 246 runs into the gapt₂. Accordingly, the weld boss 246 provided at the ceiling surface 244must be disposed near the small diameter portion 242, so that theresidue of the fused weld boss 246 does not overflow onto the outercircumferential surface of the hub 240.

As described above, in order to eliminate the risk of the edge of themagnetic tape coming into a gap, what is required is simply that no gapis formed in the area of the outer circumferential surface of the hub240 where the magnetic tape is wound. Therefore, the shape is notlimited to the above structure.

For example, as shown in FIGS. 19A and 19B, a depression 256 is providedbetween a small diameter portion 252 (stepped portion) provided at a hub250 and a ceiling surface 254. A projection 260, which can beaccommodated in the depression 256, is provided at a lower flange 258 sothat the projection 260 is accommodated in the depression 256 when thelower flange 258 is welded to the hub 250, and a gap t₃ is formedbetween the projection 260 and the depression 256.

In order to ensure that residue of a weld boss 255 provided at theceiling surface 254 runs into the gap t₃, the weld boss 255 is providednear the small diameter portion 252. Thus the residue of the weld boss255 does not overflow onto an outer circumferential surface of the hub250.

Next, a reel of a magnetic tape cartridge according to a thirdembodiment of the present invention is described. It should be notedthat details of the magnetic tape cartridge according to the presentembodiment are substantially the same as those of the magnetic tapecartridge according to the first embodiment, and therefore explanationthereof is omitted.

As shown in FIGS. 20 and 21, a reel hub 302 (core) and a lower flange304 forming a reel 300 are integrally molded. The lower flange 304 isprovided with an annular depression 306 outside the reel hub 302. Ametal sleeve 308, which serves as a hub, can be fitted in the annulardepression 306 so as to sheathe the reel hub 302.

A height of the sleeve 308 is less than a height of the reel hub 302,and a tip of the reel hub 302 sticks out from the sleeve 308 when thesleeve 308 is fitted in the annular depression 306.

A weld boss 310 for ultrasonic welding having a substantially triangularsectional form is provided so as to project from an end surface of thereel hub 302. By fusing the weld boss 310 with ultrasonic waves in astate in which an upper flange 312 is placed on the top of the weld boss310, the upper flange 312 is welded to the end surface of the reel hub302, to form the reel 300.

A boss 312A is formed at the upper flange 312. A height of the boss 312Ais equal to the difference between the height of an end surface of thesleeve 308 fitted in the annular depression 306 and the height of theend surface of the reel hub 302.

When the upper flange 312 is placed on the reel hub 302, the boss 312Afaces the annular depression 306 formed at the lower flange 304, and anouter circumferential surface of the annular depression 306 is disposedin line with an outer circumferential surface of the boss 312A.

When the upper flange 312 is welded to the end surface of the reel hub302 by ultrasonic welding as shown in FIGS. 22 and 23, the end surfaceof the boss 312A abuts on the end surface of the sleeve 308. The sleeve308 is fixed by the annular depression 306 and the boss 312A, and theouter circumferential surface of the boss 312A and the outercircumferential surface of the sleeve 308 become substantially flush.

Because the sleeve 308 is disposed at the outer circumferential surfaceof the annular depression 306, a gap is formed between the innercircumferential surface of the sleeve 308 and the outer circumferentialsurface of the reel hub 302. However, because the sleeve 308 is fixed bythe annular depression 306 and the boss 304A, the sleeve 308 does notrattle.

In the structure described above, the sleeve 308 is disposed outside thereel hub 302, and the magnetic tape 12 (see FIG. 1) is wound on thesleeve 308. Therefore, even if the reel hub 302 is caused to incline bythermal contraction after molding of the reel hub 302 and the lowerflange 304, this inclination will not affect winding of the magnetictape 12. As a result, a highly accurate hub can be obtained.

Further, thermal contraction after the molding is effected along radialdirections of the reel hub 302 and the lower flange 304, and the annulardepression 306 follows the thermal contraction of the reel hub 302 andthe lower flange 304. By providing the annular depression 306 at thelower flange 304 on a concentric circle thereof, and fitting the sleeve308 in the annular depression 306, the axis of the sleeve 308 is alignedwith axes of the reel hub 302 and the lower flange 304. Therefore, theaxis of the sleeve 308 does not deviate with respect to the lower flange304.

In a conventional structure, if a reel hub 320 is inclined by thermalcontraction of the reel hub 320 and a lower flange 322 (see FIG. 26),the inclination of the reel hub 320 will affect winding of a magnetictape, and therefore such reels have been considered defective. However,by placing the sleeve 308 outside (around) the reel hub 302, yield isimproved and this leads to a cost reduction.

It should be noted that although the lower flange 304 is provided withthe annular depression 306 and the sleeve 308 is fitted around the reelhub 302 and fitted in the annular depression 306 after the lower flange304 and the reel hub 302 are molded, other structures can also be used,as long as they can provide a highly accurate hub.

For example, by inserting the metal sleeve 308 in a metal mold formolding the lower flange 304 and the reel hub 302, these may beintegrally molded such that the sleeve 308 is positioned outside thereel hub 302. Since the metal sleeve 308 has a lower coefficient oflinear expansion than synthetic resins, it hardly deforms at allcompared with synthetic resins. Therefore, a highly accurate hub can beobtained.

However, the sleeve is not limited to the metal sleeve 308, and may bemade of any material whose melting temperature is higher than that ofthe core and the lower flange, and which does not melt when the core andthe lower flange are molded. Therefore, the sleeve may be made of asynthetic resin.

Further, as shown in FIGS. 24 and 25, by providing a small diameterportion 314A at one end side of an outer circumference of a sleeve 314,fitting the small diameter portion 314A in an annular depression 315 ofa lower flange 316, and abutting a ceiling portion between the outercircumferential surface of the sleeve 314 and the small diameter portion314A on the lower flange 316, the risk of the edge of the magnetic tape12 (see FIG. 1) coming into a gap formed between the outercircumferential surface of the sleeve 314 and the annular depression 315can be eliminated.

Further, a small diameter portion 314B may be provided at an innercircumference at the other end side of the sleeve 314 and a boss 318A ofan upper flange 318 may be positioned at the inner circumference side ofthe sleeve 314. In this structure, the magnetic tape 12 is wound only onthe sleeve 314. Therefore, even if the size of the boss 318A of theupper flange 318 is irregular, winding of the magnetic tape 12 will notbe affected.

Next, a magnetic tape cartridge according to a fourth embodiment of thepresent invention is described. It should be noted that details of themagnetic tape cartridge according to the present embodiment aresubstantially the same as those of the magnetic tape cartridge accordingto the first embodiment, and therefore explanation thereof is omitted.

As shown in FIG. 1, in the magnetic tape cartridge according to thefirst embodiment of the present invention, the annular reel gear 70formed at the top surface side of the bottom wall 58 of the reel hub 56can mesh with the braking gear 82 provided at the bottom surface outercircumferential portion of the braking member 80, which can beaccommodated in the reel hub 56. When the magnetic tape cartridge 10 isnot in use, the braking gear 82 of the braking member 80 meshes with thereel gear 70 to prevent rotation of the reel 50. However, in the presentembodiment, shown in FIGS. 27 and 28, a braking reel gear 404 isprovided at an outer circumferential portion of a lower flange 402 so asto mesh with a braking gear 410 of a braking member 408 provided in thevicinity of at least one corner within a lower case 406.

The braking member 408 is provided for preventing rotation of a reel 400when a magnetic tape cartridge 412 is not in use. The braking member 408has a substantial L shape viewed from above. The braking member 408 issupported rotatably with a lower portion of a supporting shaft 414 atthe middle of the braking member 408 being fitted, with play, around aprotrusion (not shown) provided at the lower case 406, and asubstantially cylindrical protrusion 414A provided at an upper portionof the supporting shaft 414 being fitted, with play, in a boss 405Aprovided projecting from an inner surface of an upper case 405.

The braking gear 410 is provided at one end of the braking member 408,and an engaging portion 418 is provided at the other end thereof. Theengaging portion 418 faces an opening 424 provided in a peripheral wall420 of the lower case 406. The braking gear 410 is urged against thereel gear 404 by a torsion spring 426.

Thus, the braking gear 410 engages with the reel gear 404, therebypreventing rotation of the reel 400. By providing the reel gear 404 atthe outer circumferential portion of the lower flange 402, and engagingthe braking gear 410 with the reel gear 404 to effect braking (toprevent rotation), required braking force becomes small and pitch of thereel gear 404 and the braking gear 410 can be increased.

Specifically, the pitch of the reel gear 404 and the braking gear 410 isusually in a range from 1 to 3.5 mm, and more usually from 2.5 to 3 mm.This pitch makes the reel gear 404 and the braking gear 410 resistant tobreakage, and unintended rotation of the reel 400 can be assuredlyprevented preferably.

Since the reel gear 404 is provided at the outer circumferential portionof the lower flange 402, and the braking gear 410 engages with the reelgear 404 to effect braking, there is no need to provide the reel gear 70(see FIG. 1) at a top surface of a bottom wall 428 of the reel 400.Therefore, molding accuracy of the reel 400 can be improved.

When the magnetic tape cartridge 412 is mounted in the drive 65, anengaging member (not shown) provided at the drive 65 enters the magnetictape cartridge 412 through the opening 424 and pushes the engagingportion 418 of the braking member 408, thereby rotating the braking gear410 on the supporting shaft 414, against the urging force of the torsionspring 426, in a direction in which meshing between the braking gear 410and the reel gear 404 is released.

Next, operation of the magnetic tape cartridge 412 having theabove-described structure is explained.

When the magnetic tape cartridge 412 is not in use, unintended rotationof the reel 400 is prevented by the braking member 408. Namely, thebraking gear 410 urged by the torsion spring 426 meshes with the reelgear 404 formed at the lower flange 402 of the reel 400 to preventunintended rotation of the reel 400.

On the other hand, when the magnetic tape cartridge 412 is to be used,it is mounted in a bucket (not shown) of the drive 65. When the magnetictape cartridge 412 is mounted in the bucket, the bucket moves downwardand a rotation shaft 67 of the drive 65 moves relatively closer to theopening 38.

Then, the substantially cylindrical mesh-release pin 69 provided at thecenter of the distal end of the rotating shaft 67 enters the magnetictape cartridge 412 through a hole 440A in a reel plate 440, abuts on aprojection 444 of a spring seat 442, and via the projection 444, pushesthe spring seat 442 upward against the urging force of the spring 16.The magnet (not shown) disposed at the distal end of the rotating shaft67 except at the mesh-release pin 69 attracts and holds the reel plate440, and the reel gear 60 is meshed with the driving gear 63 while thecenter of rotation is preferably secured.

At this time, the engaging member (not shown) enters the magnetic tapecartridge 412 through the opening 424 and pushes the engaging portion418 to rotate the braking gear 410 against the urging force of thetorsion spring 426 to a non-meshing position, thereby releasing themeshing between the braking gear 410 and the reel gear 404. Thus,rotation of the reel 400 is permitted.

Thereafter, the pulling pin (not shown) provided at the drive 65 isengaged with a depression 452 of the leader block 40 attached at the endof the magnetic tape 12, and pulls the leader block 40 out of themagnetic tape cartridge 412.

Then, the leader block 40 is fitted to a reel hub of a winding reel (notshown) at the drive 65 such that the magnetic tape 12 can be wound onthe winding reel. The reel 400 and the winding reel are driven to rotatesynchronously to wind the magnetic tape 12 on the winding reelsequentially, and at this time data is written on or read from themagnetic tape 12.

When the magnetic tape 12 has been completely wound up on the windingreel, the reel 400 and the winding reel are driven to rotate in areverse direction, to wind the magnetic tape 12 on the reel 400. Whenthe magnetic tape 12 has been completely wound up on the reel 400, theleader block 40 is pulled out of the reel hub and is locked at anopening 432 of the magnetic tape cartridge 412.

Then, the magnetic force of the magnet is turned off, releasing theattraction between the magnet and the reel plate 440, the rotating shaft67 is moved downward to release the meshing between the reel gear 60 andthe driving gear 63, and the mesh-release pin 69 is pulled out from thehole 440A in the reel plate 440.

Thus, the spring seat 442 is pushed downward by the urging force of thespring 16. Also the engaging member is retracted from the opening 424formed in the lower case 406, releasing the pressure applied onto theengaging portion 418. Thus, the braking gear 410 is meshed with the reelgear 404 by the urging force of the torsion spring 426 to preventunintended rotation of the reel 400, as described above.

It should be noted that, although in this embodiment the reel gear 404is provided at the outer circumferential portion of the lower flange 402and is engaged with the braking gear 410, a braking reel gear may beprovided at the upper flange 430 and for engaging with a braking member.

In the invention exemplified by the first embodiment, by forming the hubso that sectional forms thereof taken radially from the axis thereof arethe same, flowing states of the molding material at the respectivecross-section positions can be made the same at the respectivecross-sectional positions. Therefore, the flowing state of the moldingmaterial does not differ with circumferential direction position.

Often in the invention, by joining the outer circumference of theinserted metal plate to the end of the hub by an annular joining device,sectional forms of the hub taken radially from the axis can be made thesame as each other. Further, since there is no need to provide holes orthe like in the metal plate, as there has been in prior arts, variationsin the pressure of the molding material flowing over the metal plate aresmall. Therefore, residual stress can be reduced, thereby improvingaccuracy of the hub and flatness of the flange. Furthermore, by joiningat the outer circumference of the metal plate, the internal dimensionsof the portion joining the metal plate are increased compared with thecase in which the metal plate is provided with holes. This means air isremoved easily and is less likely to be retained. Thus, no wrinkles arecreated on the hub and the flange.

Often in the invention, the joining portion is formed as an annular pawlportion. Therefore, the metal plate is prevented from detaching. In theinvention, the metal plate can be firmly fixed to the hub. Also, themetal plate can be fixed within the metal mold with certainty.

In the invention exemplified by the second embodiment, the hub and theflange are separately molded. This allows selection of a suitable gatingsystem (e.g., disc gates) and setting of optimal molding conditions foreach shape. Therefore, compared with the case in which the hub and theflange are integrally molded, variations in pressure at the hub can bereduced and flatness of the flange can be improved. Further, roundnessof the hub can be improved together with the improvement in the flatnessof the flange. Moreover, by welding, the hub and the flange can beunited with certainty and without backlash, compared with the case inwhich the flange and the hub are provided with pawl portions for fittingto each other, and can be united more simply compared with the case inwhich the flange and the hub are threaded and screwed together.

Often in the invention, by providing a first weld boss and a second weldboss projecting from the welding surfaces, the first weld boss and thesecond weld boss fuse to weld the flanges to the hub when frictionalheat is generated between the flanges and the hub by vibrational energyof an ultrasonic welder. Therefore, compared with the case in which noweld boss is provided, these parts can be welded together more firmly.

Often in the invention, by forming a gap between the innercircumferential surface of the flange and the outer circumferentialsurface of the collar and the hub, and making residue from the weldingsurface run into the gap, the residue of the welding can be preventedfrom running onto the surface of the flange. In the invention, a gap maybe formed between the wall surface of the stepped portion and the outercircumferential surface of a boss provided at the inner circumferentialportion of the flange, and the residue of the second weld boss made torun into the gap there. Also, the edges of the recording tape can beprevented from entering such gaps.

In the invention exemplified by the third embodiment, the hub is placedoutside the core and the recording tape is wound on the hub. Therefore,even if the core is inclined due to thermal contraction after molding ofthe core and the lower flange, the inclination does not affect thewinding of the recording tape, and a highly accurate hub can be obtainedas a result.

Often in the invention, during the thermal contraction after themolding, the thermal contraction is effected along the radial directionsof the core and the lower flange. Therefore, an annular depressionfollows the thermal contraction of the core and the lower flange. Byproviding the annular depression at the lower flange on a concentriccircle thereof, and fitting a sleeve of the hub in the annulardepression, the axis of the sleeve is aligned with axes of the core andthe lower flange. Therefore, the axis of the sleeve does not deviatewith respect to the lower flange.

Often in the invention, a shoulder portion between a small diameterportion and a large diameter portion abuts on the lower flange.Therefore, even if a gap is formed between the small diameter portionand the annular depression, the recording tape does not come into thegap. More usually in the invention, a labor for attaching the sleeveafter the molding of the core and the lower flange can be saved.Therefore, production processes can be reduced, thereby reducingproduction costs.

Often in the invention, since a metal has a lower coefficient of linearexpansion than synthetic resins and hardly deforms, use of the metalsleeve provides a highly accurate hub. More usually in the invention,the recording tape 12 is wound only on the sleeve. Therefore, even ifthe size is irregular at engaging portion which engages with the sleeveat the upper flange or the lower flange, this does not affect thewinding of the recording tape.

In the invention exemplified by the fourth embodiment, by providing abraking gear at the outer circumference of the flange to effect braking,unintended rotation of the reel when the recording tape cartridge is notin use can be prevented with certainty. Further, compared with the casein which the braking gear is provided at the core side of the flange,the required braking force is smaller and the pitch of the braking gearcan be increased. Therefore, failures such as breakage of the brakinggear are not caused. Moreover, since the braking gear is not provided atthe core side of the flange, molding accuracy of the reel can beimproved.

Often in the invention, since a braking member urged by an urging devicemeshed with the braking gear when a driving gear is not meshed with arotation gear, the reel cannot rotate in this state. When the drivinggear meshes with the rotation gear, the braking member can be pushedagainst the urging force of the urging device and the engagement betweenthe braking member and the braking gear released. Thereafter, drivingforce from the driving gear is transmitted to the reel rotation gear torotate the reel. Usually in the invention, the braking gear does noteasily break.

1. A recording tape cartridge for rotatably accommodating a reel onwhich a recording tape is wound, the reel comprising: a hollow hub onwhich the recording tape can be wound, the hub including two ends; afirst annular flange welded at one end of the hub for retaining onewidth-direction end of the recording tape wound on the hub; and a secondannular flange welded at the other end of the hub for retaining anotherwidth-direction end of the recording tape wound on the hub, wherein theone end of the hub comprises a collar portion including, along acircumferential direction thereof, a surface for welding to the firstannular flange, the surface having been provided with a first weld bossprotruding therefrom, and the other end of the hub comprises a steppedportion including, along a circumferential direction thereof, a surfacefor welding to the second annular flange, the surface having beenprovided with a second weld boss protruding therefrom.
 2. The recordingtape cartridge according to claim 1, wherein the collar portion includesan outer circumferential surface and the first annular flange includesan inner circumferential surface, which surfaces form therebetween a gapfor receiving residue of the first weld boss, and the hub includes anouter circumferential surface and the first annular flange furtherincludes another inner circumferential surface, which surfaces formtherebetween another gap for receiving residue of the first weld boss.3. The recording tape cartridge according to claim 1, wherein the secondannular flange includes an inner circumferential portion provided with aboss which includes an outer circumferential surface, the steppedportion includes a wall surface, and the surfaces form therebetween agap for receiving residue of the second weld boss.
 4. A recording tapecartridge for rotatably accommodating a reel on which a recording tapeis wound, the reel comprising: a hollow hub on which the recording tapecan be wound, the hub including two ends; a first annular flange weldedat one end of the hub for retaining one width-direction end of therecording tape wound on the hub; and a second annular flange welded atthe other end of the hub for retaining another width-direction end ofthe recording tape wound on the hub, wherein the one end of the hubincludes a wall surface and a ceiling portion, the first annular flangeincludes a stepped portion which engages with the one end of the hub,the stepped portion includes a top surface having been provided with athird weld boss protruding therefrom, the top surface making surfacecontact with the ceiling portion, and the stepped portion includes aninner circumferential surface, the inner circumferential surface and thewall surface forming therebetween a gap for receiving residue of thethird weld boss, and the other end of the hub comprises a steppedportion including, along a circumferential direction thereof, a surfacefor welding to the second annular flange, the surface including a secondweld boss protruding therefrom.